Casing Plug

ABSTRACT

A dissolvable plug for plugging oil and gas well casings to perform treatment and other downhole operations is disclosed. The plug is attached to a setting tool and lowered downhole. The setting tool is fired to cause the plug to engage the casing and to release the setting tool. A ball is dropped to close the passage through the plug. Hydraulic pressure is applied on the ball from above and the plug expands outwards to create a seal between the plug and the casing. After operations above the plug are completed, the ball and the plug are dissolved by the surrounding fluids.

RELATED PRIORITY DATE APPLICATION

This application claims the benefit under 35 U.S.C. 119(e) of the U.S.provisional application No. 62/691,588 filed on Jun. 28, 2018.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of oil tools for thecompletion of oil and gas oils and, more particularly, to the field ofcasing plugs. Still more particularly, the present invention discloses acasing plug constructed of dissolvable material so that the plug may bedissolved after it is used downhole to reestablish communication aboveand below the plug without mechanical intervention from the surface.

BACKGROUND OF THE INVENTION

The use of plugs and packers in downhole oil and gas operations are wellknown. During completion or well intervention, a plug is used to isolatea part of the casing from another part. For instance, when a job iscarried out on the upper section of the well, the lower part of theinterior of the casing must be isolated and plugged, i.e. zonalisolation in a well. Plugs can be temporary or permanent; the former canbe retrieved, whereas the latter have to be drilled out. Plugs can heset using a wire-line, coiled tubing or drill pipe.

One disadvantage of the plugs presently used is that they requiremechanical intervention from above to retrieve them or to drill throughthem to reestablish flow through the casing. These practices causedelays and additional expenses.

According to the present invention, a dissolvable plug is disclosedwhich can be dissolved downhole following completion of the operationsto reestablish the flow through the casing without requiring mechanicalintervention from above to retrieve or to drill the plug.

These and other advantages of the present invention will become apparentfrom the following description.

SUMMARY OF THE INVENTION

A dissolvable plug for plugging oil and gas well casings to performtreatment and other downhole operations is disclosed. The plug includesan upper sub, a lower sub and a slip assembly. The upper sub includes aflow passage with a tapered mouth, and a circumferential exterior ramp.

The lower sub includes an axial bore. The slip assembly has a chamferedend and ceramic buttons on its exterior and is disposed over the uppersub. In the assembled position, the slip assembly is slidingly disposedover the upper sub and its chamfered end intimately engages the ramp onthe exterior of the upper ramp. The lower end of the upper sub isreceived in the upper end of the bore of the lower sub. The lower sub isconnected to the upper sub by shear screws.

In operation, the plug is attached to a wireline setting tool whichincludes a setting tool sleeve, a setting tool adopter and a shearadapter by shear screws connecting the shear adopter to the lower sub.The setting tool and the attached plug are lowered downhole to be set atthe desired location inside the casing.

When the plug reaches the desired setting depth in the casing thesetting tool is fired. The setting sleeve holds the upper sub in placewhile the shear adapter pulls up the lower sub causing the shear screwsconnecting the upper sub to the lower sub to shear. As the lower sub ispulled upwards, it causes the slip assembly to expand outwards and toengage the casing. In that position, the lower sub becomes locked to theupper sub by locking threads. Then, the remaining setting force shearsscrews connecting the shear adapter to the bottom sub and the settingtool is released and raised to the surface.

After the setting tool is raised to the surface, a ball is pumpeddownhole to rest in tapered mouth of the upper scab and to close thepassage therethrough. Pressure is applied on the ball to extrudeoutwards the upper portion of the upper sub thereby tightening the sealagainst the casing. The zone inside the casing above the plug is nowisolated and various perforations and treatment operations are performedtherein.

The plug and the ball are constructed of material which are dissolvableafter a certain amount of time following exposure to the surroundingfluids, the amount of time being depended on the temperature andsalinity of the liquids. After the treatment operations are completed,the plug and the ball begin to dissolve thereby reopening the passagethrough the casing without intervention from the surface to remove theplug. Preferred dissolvable material are magnesium alloys and degradablesealing elements. Other dissolvable material may be used to constructthe plug and the ball

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiment of the invention,reference will now be made to the accompanying drawings wherein:

FIG. 1 is a cross sectional view of a plug made in accordance of thepresent invention along the axis A-A of the plug of FIG. 3;

FIG. 2 is a perspective view of the plug of FIG. 1;

FIG. 3 is a bottom view of the plug of FIG. 1;

FIG. 4 is a cross sectional view of the plug of FIG. 1 attached to asetting tool;

FIG. 5 is a perspective view of the plug and setting tool of FIG. 4; and

FIG. 6 is a cross sectional view of the plug of FIG. 1 followingactivation providing a seal in a casing downhole.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 there is shown a plug 10 that includes an upper sub12, a lower sub 14 and a slip assembly 16. Upper sub 12 includes aninternal axial flow passage 20 with a tapered mouth 22, an exteriorcircumferential groove 24 adjacent to mouth 22, a circumferentialexterior ramp 26, a plurality of radial screw sockets 28 and a pluralityof grooves 32 circumferentially disposed over the lower portion of uppersub 12. Upper sub 12 further includes an upper sub locking thread (notshown) on its exterior surface that will engage a corresponding lowersub locking thread in lower sub 14 when lower sub 14 is moved to alocking position as described below. An elastomeric ring 36 is disposedin circumferential groove 24.

Lower sub 14 includes an axial bore 36, a plurality of radial screwsockets 38 circumferentially disposed in the upper portion of lower sub14, and a plurality of radial screw sockets 42 circumferentiallydisposed in the lower portion of lower sub 14. Lower sub 14 furtherincludes a lower sub locking thread (not shown) on its interior wall ofbore 36 which is lockingly engageable with the upper sub locking threadwhen lower sub 14 is moved to a locking position.

Slip assembly 16 is a generally tubular member having a chamfered end 46and a plurality of ceramic buttons 56 drilled in the exterior thereof.In the assembled position slip assembly 16 is slidingly disposed overthe lower portion of upper sub 12 and chamfered end intimately engagesconforming ramp 16. The lower end of upper sub 12 is intimately receivedin the upper end of bore 36 to align screw sockets 28 and 38. Shearscrews 50 are inserted in sockets 28 and 38 to securely connect uppersub 12 to lower sub 14.

Referring now to FIG. 2 there is shown a perspective view of plug 10having an upper sub 12, a lower sub 14 with radial screw sockets 42 anda slip assembly 16 having buttons 56.

Referring now to FIG. 3, there is shown a bottom view of plug 10 in theassembled position having lower sub 14 with radial screw sockets 42 andupper sub 12 received in lower sub 14.

Referring now to FIG. 4, plug 10 is attached to a wireline setting tool60 such as a Baker 10 setting tool. Setting tool 60 includes a settingtool sleeve 62 abutting the top of upper sub 12, a setting tool adapter64 and a shear adapter 70 having screw sockets 72. Screw sockets 72 arealigned with radial screw sockets 42 and shear screws 74 are insertedtherein to securely connect shear adapter 70 to lower sub 14. Plug 10attached to setting tool 60 is lowered downhole to be set at the desiredlocation inside the casing. Referring now to FIG. 5 there is shown aperspective view of setting tool connected to plug 10.

Referring back to FIG. 4, when plug 10 reaches the desired setting depthin a casing, setting tool 60 is fired. Setting sleeve 62 holds upper subin place while shear adapter 70 pulls up lower sub 14 up causing shearscrews 50 to shear. As lower sub 14 is pulled upwards, it advances slipassembly 16 to ride on ramp 26 whereby it is pushed outwards to engagethe casing. In that position, the lower sub locking thread and the uppersub locking thread described above are lockingly engaged. After slipassembly 16 engages the casing and the two locking threads engage eachother, the remaining setting force shears screws 74 that hold shearadapter 70 to bottom sub 14 and setting tool 60 is released and raisedto the surface.

Referring now to FIG. 6, there is shown plug 10 with slip assembly 16engaging a casing 78. After setting tool 60 (not shown) is raised to thesurface a ball 80 is pumped downhole to rest in tapered mouth 22 insideupper sub 12 and to close passage 20. Pressure is applied on ball 80 toextrude outwards the upper portion of upper sub 12 thereby tighteningthe seal against casing 78. The zone inside casing above plug 10 is nowisolated and various perforations and treatment operations are performedtherein. As shown, plug 10 is designed to hold pressure from above only.

According to the present invention, plug 10 and ball 80 are constructedof material which are dissolvable after a certain amount of time whenthey are exposed to the fluids flowing in the zone during the treatmentoperations. The amount of time after which the material beginsdissolving depends on the temperature and salinity of the water downholearound plug 10. According to the invention, after the treatmentoperations are completed, plug 10 and ball 80 begin to dissolve and theseal to casing 78 is lost whereby more fluid flows through and aroundplug 10 and ball 80 further effecting and completing the dissolution ofplug 10 and ball 80. Accordingly, because plug 10 and ball dissolve, nointervention from the surface is required to remove plug 10. Thematerial are selected so as to begin dissolving after a certain time,preferably after 24 to 48 hours, following the start of the perforationand treatment operations downhole in the zone above plug 10.

Preferred dissolvable material are dissolvable magnesium alloys such asthe ones being sold by Bubbletight under the trademark Magnalloy anddegradable sealing elements sold also by Bubbletight. It should beunderstood, however, that other dissolvable material may be used toconstruct plug 10 and ball 80 as long as they can withstand thepressures downhole while conducting the operations in the zone aboveplug 10.

The locking screws are preferably constructed of brass material.Further, instead of ceramic buttons 56, slips with wickers or bidirectional slip may be used on slip assembly 16.

While the invention is described with respect to specific embodiments,modifications thereof can be made by one skilled in the art withoutdeparting from the spirit of the invention. The details of saidembodiments are not to be construed as limitations except to the extentindicated in the following claims.

What is claimed is:
 1. A plug for sealing a casing having an innersurface, comprising: a first member having a sealing member; a slidablesecond member connected to the first member; and a third member slidableover the first member; the first, second and third members beingdissolvable after a certain amount of time.
 2. A plug for sealing acasing having an inner surface, comprising: a first member having asealing member; and a slidable second r connected to the first member;the first, second and third members being dissolvable after a certainamount of time.